This book synthesizes, with some additions, Gat’s 800-page War and Civilization in a readable volume. With new material on Australian aborigines, the book begins by making a convincing case for the deep roots of war in human prehistory (vindicating Hobbes over Rousseau). It ends with a solid argument for treating the decline of war as a process – the Modernization Peace – embedded in industrialization over the past two centuries. This trend, Gat argues, arises not because war is becoming more expensive but because peace is becoming more rewarding. (Threats to the modernization peace remain, however.) Between these two contributions, the book pushes a theory on the causes of war based in evolutionary biology. Its strength and weakness are the same: fitting complex realities into simple theoretical constructs. Gat’s strongest argument here is that war is purposeful and useful, historically, rather than senseless and tragic. But although he delivers a coherent argument that readers will find thought-provoking, it is far from compelling, especially with regard to the sexual rewards of conquest and their claimed evolutionary consequences. The weakest two chapters consist of slashing attacks on straw-men representing the fields of anthropology and international relations (IR) theory, respectively, with each chapter reflecting incomplete familiarity with the discipline’s literatures. The book’s first page dismisses the entire IR literature on the causes of war with a single long footnote. These parts of the book suffer from the effort to condense and cover too much ground superficially. Nonetheless, for readers deterred by the length of War and Civilization, or those who enjoyed it and want more, Gat delivers a well-written and thoughtfully argued volume.